To spread crack for a tap from some johnson you've dumped, usually inducing a shame spiral. Note: only women and gay men can backslide, since straight men will screw anything, anytime, without remorse.

Johnny: You look like shit.
Eric: My ex came over last night.
Johnny: You backslide?
Eric: You know it.
Johnny: That must be some good rod.
Eric: Better than that take-out you scarf.